The present invention relates to a molded polyurethane body having high light fastness as well as improved temperature stability.
German Published Patent Application Nos. 26 58 136 and 42 03 307 describe thermoplastic, processable molding materials are made of mixtures of different aliphatic polyols and 1,6 hexamethylene diisocyanate having chain lengthening means such as 1,4 butane diol. The polyurethane molding materials described can be used, in particular, for manufacturing food packaging, but also for manufacturing films for decorative purposes.
However, using such polyurethane molding materials in the interior of motor vehicles is not guaranteed due to the automobile industry""s increased demands on the materials used to produce dashboard coatings, according to which these materials must possess grain stability and hot-light stability of at least 130xc2x0 C.
Also for use as food packaging or as molded bodies for hygienic or medicinal purposes, the ability to sterilize using superheated steam is not sufficient.
It is an object of the present invention to provide a molded polyurethane body and a method for its manufacture and use, the molded body having high hot-light fastness as well as improved dimensional heat stability.
These and other beneficial objects of the present invention are achieved by providing a molded polyurethane body obtained by reacting: a) one or more aliphatic polyols having a molecular weight of 450 to 6000 g/mol and an hydroxyl value of 10 to 235; with b) aliphatic and/or cycloaliphatic diisocyanates in an equivalent ratio of diisocyanate to polyol of 1.2:1.0 to 16.0:1.0; with c) diols as chain lengthening agents having a molecular weight of 60 to 450 g/mol, the NCO index formed from the quotient, which is multiplied by 100, of the equivalent ratio of isocyanate groups to the sum of the hydroxyl groups of polyol and chain lengthening agents lying within a range of 90 to 105; and with d) an at least bifunctional reaction component, which is suitable for subsequent cross-linking, and which reacts with the terminal hydroxyl groups of the polyurethane chain as well as with the acidic hydrogen atoms of the urethane groups and leads to branched-chain reactions, the thermoplastic polyurethane formed by conversion from the components a) through c) in a first step being homogenously mixed in a second step with 0.2 to 25 parts by weight of component d) with respect to 100 parts by weight of the thermoplastic polyurethane, formed into a molded body, and subsequently cross-linked at temperatures from 80 to 240xc2x0 C.
It has been discovered that aliphatic, linear, long-chain, thermoplastic polyurethanes are significantly improved by adding a latently reactive cross-linking component that under processing conditions at increased temperatures results in a higher molecular, branched polyurethane. In particular, the molded polyurethane bodies according to the present invention have higher temperature stability, hot-light stability, as well as dimensional heat stability, which are mirrored in the following advantageous properties:
improved processability in thermoplastic manufacturing processes, such as injection molding, melt extrusion, melt spinning methods, sintering methods, hot-melt adhesive methods.
improved crystallization properties, particularly quick recrystallization for an economical manufacturing process in the aforementioned methods.
high tensile strength, tear initiation strength, and resistance to further tearing.
improved elastic properties.
According to the present invention, molded polyurethane bodies are manufactured in that a thermoplastic polyurethane molding material is produced from components a) through c) recited above and well homogenized in a powdered or granular form with component d) recited above, and in that the homogenized material is formed into a molded body and subsequently cross-linked at temperatures of 80 to 240xc2x0 C. The thus manufactured molded polyurethane body possesses improved physical properties and elastic properties and high light fastness. Furthermore, they are dimensionally stable up to at least 150xc2x0 C., i.e., they do not show any changes in grain stability when used as surface materials.
Preferably, the molded polyurethane bodies are produced in that component d) is applied in a liquid, paste-like, or solid form at room temperature in a tumbling mixer by tumbling on the thermoplastic, polyurethane molding material obtained from components a) through c). The shelf life of the mixture of thermoplastic, polyurethane molding material and cross-linking component d) depends on their reactivity. A mixture of a liquid, aliphatic diisocyanate or triisocyanate may, for example, be processed as a cross-linking component within 24 hours storage time at room temperature under the same processing conditions in the thermoplastic method, while mixtures having solid, dimeric isocyanates or end-group-blocked isocyanates as cross-linking components are stable in storage at room temperature for several months. The mixture of the thermoplastic, polyurethane molding material obtained from components a) through c) and from cross-linking component d) is processed in a thermoplastic method at an increased temperature. As a result of the thermoplastic polyurethane and the cross-linking component simultaneously fusing and flowing together, an additional intimate mixture of components is attained. The cross-linking component is activated at the increased temperatures, and as a result, the active hydrogen groups are subsequently cross-linked by urethane bonds such as hydroxyl groups. The transformation to the molded polyurethane body according to the present invention and having increased dimensional heat stability is completed according to the reactivity of the cross-linking component either immediately following the manufacturing process or first after several days of storage time.
The molded polyurethane bodies obtainable according to the present invention do not have any mechanical or process engineering disadvantages with respect to conventional aliphatic thermoplastically processable polyurethane molding materials, as the following examples show. In the application according to the present invention as surface materials, the molded polyurethane bodies include the following advantages:
dry, leather-like feel.
improved resistance to solvents and cleaning agents.
reduced sensitivity to scratches.
improved resistance to abrasion.
Furthermore, in their use as a hot-melt adhesive or an adhesive material for textile purposes, the molded polyurethane bodies according to the present invention exhibit:
improved fastness to washing and cleaning.
improved adhesion at higher temperatures.
During their manufacture, the molded polyurethane bodies according to the present invention may be mixed with conventional filler agents and loading materials, flameproofing agents and anti-ageing agents, as well as processing aids and pigments.
The invention is described further with reference to the following examples: